Prevention strategies have been developed to take advantage of the metabolic and behavioral risk factors for NIDDM which have been identified in research with the Pima Indians and elsewhere. Obesity, impaired glucose tolerance, hyperinsulinemia, physical inactivity, and high fat diet have been implicated as risk factors for NIDDM. Since these factors are potentially reversible with behavioral and pharmacologic therapy, strategies for prevention have been developed and will be tested. This project is a multicenter randomized clinical trial of prevention of non-insulin-dependent diabetes mellitus in overweight persons with impaired glucose tolerance known as the Diabetes Prevention Program. The coordinating center is at the George Washington University. During the project year implementation of the program was begun in four American Indian communities in collaboration with the Indian Health Service.